Experimental Physics and
Industrial Control System

Alan Kastengren <[email protected]> · Mon, 30 Jan 2017 09:59:40 -0600

 I am trying to get a development machine on Linux RHEL 7 configured

so I can work on PyEpics scripting, and I am having some difficulties.

I have installed EPICS base 3.14.12.6 and set the PYEPICS_LIBCA,

EPICS_BASE, and EPICS_HOST_ARCH environment variables. I'm using the

Anaconda Python distribution (version 2.7 of Python) on a local install

on my machine (since it's a laptop and won't always have access to

APSshare). I installed PyEpics through conda (version 3.2.6), as

described on the PyEpics website for installation instructions. I can

perform caput and caget from the Bash shell, so I believe EPICS itself

is working correctly.

 My problem is that if start an interactive Python session I can

import epics and perform caput and caget, instantiate a PV object, etc

just fine. If I try to run the exact same commands from a script, I can

still import epics without an error, but I get the error shown below

whenever I first try to do either a caget or instantiate a PV object.

I've confirmed that the runtime is looking in the same location for the

library file in both the interactive session and the script, and that

both have the same sys.path (except for the local directory being on the

path for the scripted version) and Python version. I'm really at a loss.

Traceback (most recent call last):

 File

"/home/akastengren/anaconda2/lib/python2.7/site-packages/epics/ca.py",

line 215, in initialize_libca

    libca = load_dll(dllname)

 File "/home/akastengren/anaconda2/lib/python2.7/ctypes/__init__.py",

line 440, in LoadLibrary

    return self._dlltype(name)

 File "/home/akastengren/anaconda2/lib/python2.7/ctypes/__init__.py",

line 362, in __init__

    self._handle = _dlopen(self._name, mode)

OSError: /home/akastengren/anaconda2/bin/../lib/libreadline.so.6:

undefined symbol: PC

Traceback (most recent call last):

 File

"/home/akastengren/Python/workspace/PyEpics_Scripting/Test_install.py",

line 9, in <module>

    print(epics.caget('7bmb1:m1.VAL'))

 File

"/home/akastengren/anaconda2/lib/python2.7/site-packages/epics/__init__.py",

line 81, in caget

    thispv = get_pv(pvname, connect=True)

 File

"/home/akastengren/anaconda2/lib/python2.7/site-packages/epics/pv.py",

line 39, in get_pv

    context = ca.current_context()

 File

"/home/akastengren/anaconda2/lib/python2.7/site-packages/epics/ca.py",

line 362, in wrapper

    initialize_libca()

 File

"/home/akastengren/anaconda2/lib/python2.7/site-packages/epics/ca.py",

line 217, in initialize_libca

 raise ChannelAccessException('loading Epics CA DLL failed: ' +

str(exc))

epics.ca.ChannelAccessException: loading Epics CA DLL failed:

/home/akastengren/anaconda2/bin/../lib/libreadline.so.6: undefined

symbol: PC

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System